1. Field of the Invention
This invention relates to methods of mounting coils on rotors of rotary electric machines, and more particularly to methods of winding and mounting superconductive coils on rotors of superconductive rotary electric machines.
2. Description of the Prior Art
The electrical resistance of certain metals, such as lead, vanadium, and tin, and alloys, such as niobium-tin, becomes vanishingly small, i.e., they become superconductive, when the temperature falls below the transition temperatures thereof which are in the neighbourhood of a few degrees above absolute zero. Thus, if the field coils of an alternating current generator, for example, are formed of a superconductive material and are cooled below the transition temperature thereof, large magnetic fields can be established without the expenditure of appreciable amounts of electrical energy. When the field coils are mounted on the rotor of an alternating current generator, however, it is of paramount importance to securely mount the coils on the rotor, for the displacement of the superconductive field coils due to the movement of the rotor may generate frictional heat which destroys the superconductivity of the field coils. The fact that the superconductive field coils should be covered many times for the purpose of preventing outside heat from entering thereinto makes the reliable and secure mounting of the field coils all the more important, for such complicated structures covering the field coils make the checking and repairing of the field coils difficult to carry out.
Thus, it has been proposed to mount the superconductive field coils in corresponding grooves formed on the surface of the cylindrical coil-carrying shaft, and to securely hold the field coils in the grooves with a plurality of wedges fitted into the grooves above the field coils. The portions of the grooves running in the circumferential direction of the coil-carrying cylinder, however, have the form of partial annuli, and the wedges covering those portions of the grooves are curved, so that their machining requires much time and labour, and such precision machining is hard to attain. Further, the coils have conventionally been directly wound along the surface of the coil-carrying cylinder, bending each turn of the winding of the coil along the coil-carrying shaft. The field coils, however, have as many as several thousand turns in each winding thereof, and the superconductive linear wires from which the field coils are formed can not endure extreme bending deformation. Thus, the winding of the coils on the coil-carrying cylinder requires much labour and time, and imposes a psychological burden on the workers involved.